Flow regulator valves are typically used to balance the flow rate of water to and from heating and cooling coils when several coils are supplied from one pump incorporating many branches in the flow circuit. For this reason, the valves are typically called balancing valves because they balance the flow rate of water to each coil, although they are often used to balance flow control rates for other applications. The valves are most often used to control the flow rates of fluids with viscosities similar to that of water to fixed flow rates with variations in pressure drop across the valves. Without a flow regulation valve, as the pressure drop across a fixed orifice is increased, the flow rate is increased accordingly.
Prior-an devices have been used to achieve flow regulation by employing a squat rubber "torpedo" (resilient diaphragm), as in U.S. Pat. No. 3,189,125 ("the '125 patent"). The torpedo is forced against a contoured orifice as the pressure drop increases across the valve. Increasing pressure drops across the device will progressively press the torpedo against the contoured orifice, causing the flow area between the torpedo and the contour to be reduced. The reduction in flow area is sufficient to restrict the flow to a more-or-less constant value even though the pressure drop across the flow area has increased (see FIG. 14 of the '125 patent). However, many of the existing balancing valves utilize ribs that are molded onto the torpedo to keep it concentrically centered in the flow path immediately upstream of the contoured orifice. See, e.g., U.S. Pat. Nos. 5,027,861; 4,986,312; 3,189,125 and 3,958,603. The fluid first flows around the front of the torpedo, then through the annular section between the walls of the flow passage and the torpedo. Next, the fluid is diverted into the flow section between the torpedo and the contoured orifice (the variable flow area section) then exits out the back of the contoured orifice.
A limitation to the prior-art control devices is that they require approximately 10 pounds per square inch of pressure drop to start to control the flow rate to a fixed value (within the flow tolerance of the device). An initial pressure drop of at least four pounds would be closer to the ideal low end of the range within which a valve should operate to regulate flow. Lower required pressure drops help to reduce the required pump size, which conserves energy costs and reduces the purchase price of the pump. A large portion of the pressure drop that occurs before the device controls the flow is caused by the restriction in the annular space between the torpedo and the flow line walls. The tight 90-degree bend that the fluid must take to enter the variable flow area also creates an unnecessary restriction.
The annular space could be increased and hence reduce the pressure losses by simply making the ribs that center the torpedo larger and increasing the inside diameter of the walls of the flow passage. The problem with this approach is that the longer ribs would be too flimsy to accurately center the torpedo over the contoured orifice.
Other prior art valves are constructed of rubber elements that bend to restrict flow. For example, U.S. Pat. No. 4,986,312 discloses a flow control device utilizing a rubber disk that bends as flow increases through its center. However, most of these devices are subject to excessive bending-beam creeping and, thus, inaccuracies over time.
The orifice contours are also not ideally conducive to small pressure drops across the valve. Also, during backflow conditions, such as when backflushing a system, the prior art valves may not allow fluid to freely pass in a reverse direction, or the torpedo may become dislodged.